U.S. patent number 5,216,325 [Application Number 07/469,898] was granted by the patent office on 1993-06-01 for spark gap device with insulated trigger electrode.
This patent grant is currently assigned to Magnavox Government and Industrial Electronics Company. Invention is credited to Timothy B. Bonbrake, Barry L. Driscoll, Chiman R. Patel.
United States Patent |
5,216,325 |
Patel , et al. |
June 1, 1993 |
Spark gap device with insulated trigger electrode
Abstract
An improved solid state spark gap for use, for example, in
firing munitions. The spark gap is formed by depositing a trigger
electrode on a dielectric substrate, precisely covering the trigger
electrode and an adjoining area with a dielectric layer, and
forming an anode and a cathode on the dielectric layer with a spark
gap there between. The anode and cathode do not overlap the trigger
electrode. The spark gap may be enclosed within a hermetically
sealed inert gas filled cover.
Inventors: |
Patel; Chiman R. (New Haven,
IN), Bonbrake; Timothy B. (Fort Wayne, IN), Driscoll;
Barry L. (Fort Wayne, IN) |
Assignee: |
Magnavox Government and Industrial
Electronics Company (Fort Wayne, IN)
|
Family
ID: |
23865469 |
Appl.
No.: |
07/469,898 |
Filed: |
January 24, 1990 |
Current U.S.
Class: |
313/595; 313/308;
313/601 |
Current CPC
Class: |
H01T
2/02 (20130101); F42C 19/06 (20130101) |
Current International
Class: |
H01T
2/00 (20060101); H01T 2/02 (20060101); H01J
007/30 (); H01J 017/12 () |
Field of
Search: |
;313/595,596,130,308,603,601 ;361/120 ;102/202.5,202.7,202.9 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Triggered Multichannel Surface Spark Gaps", by H. M. von Bergmann,
Journal of Physics E. Scientific Instruments, vol. L5, No. 2, Feb.
1982, Dorking, GB, pp. 243-247..
|
Primary Examiner: DeMeo; Palmer C.
Attorney, Agent or Firm: Rickert; Roger M. Seeger; Richard
T.
Claims
We claim:
1. A spark gap device comprising a dielectric substrate, a first
electrically conductive layer on said substrate forming a trigger
electrode, a dielectric layer on said substrate covering said
trigger electrode and a predetermined adjacent area of said
substrate, separate electrically conductive layers on predetermined
portions of said dielectric layer forming a separate anode and
cathode, said anode and cathode having a predetermined spacing
defining a relatively narrow spark gap of a length greater than
that of the trigger electrode, and wherein said spark gap extends
over said dielectric layer opposite said trigger electrode and
wherein said anode and cathode extend over said dielectric layer
opposite said substrate.
2. A spark gap device, as set forth in claim 1, and further
including a cover enclosing said spark gap.
3. A spark gap device, as set forth in claim 2, wherein said cover
is a ceramic cover fused to said anode, said cathode, said
dielectric layer and said substrate.
4. A spark gap device, as set forth in claim 3, wherein said cover
is filled with an inert gas.
5. In combination with a circuit mounted on a dielectric substrate,
a spark gap device for use with said circuit comprising a first
electrically conductive layer on said substrate forming a trigger
electrode, a dielectric layer on said substrate covering said
trigger electrode and a predetermined adjacent area of said
substrate, further electrically conductive layers on predetermined
portions of said dielectric layer forming a separate anode and
cathode, said anode and cathode having a predetermined spacing
defining a spark gap, and wherein said spark gap extends over said
dielectric layer opposite said trigger electrode and wherein said
anode and cathode extend over said dielectric layer opposite said
substrate.
6. The combination of claim 5 wherein the dimension of said trigger
electrode in the direction of the predetermined spacing is less
than said predetermined spacing, and the anode and cathode are
generally symmetrically positioned relative to the trigger
electrode so that neither the cathode nor the anode extends over
the trigger electrode.
7. A spark gap device comprising a dielectric substrate, a first
electrically conductive layer on said substrate forming a trigger
electrode, a dielectric layer on said substrate covering said
trigger electrode and a predetermined adjacent area of said
substrate, separate electrically conductive layers on predetermined
portions of said dielectric layer forming a separate anode and
cathode, said anode and cathode having a predetermined spacing
defining a spark gap of a length greater than that of the trigger
electrode, and wherein said spark gap extends over said dielectric
layer opposite and beyond said trigger electrode and wherein said
anode and cathode extend over said dielectric layer opposite said
substrate.
Description
TECHNICAL FIELD
The invention relates to spark gaps and more particularly to a
solid state spark gap for discharging, for example, a capacitor
charged to a high voltage to fire a munitions fuze.
BACKGROUND ART
In certain fuze applications, munitions are fired by rapidly
discharging to the fuze energy from a capacitor charged to a high
voltage. The rapid discharge from the capacitor creates a high
current flow to a fuze. A device called a spark gap is sometimes
used to conduct a large amount of current when a specified voltage
is applied. The spark gap must conduct current at a given threshold
voltage, but must not conduct current at a lower operating voltage.
Two spark gap type devices are currently in use for firing
munitions, namely, a silicon controlled rectifier (SCR) and a gas
discharge tube. The SCR is a solid state device having an anode, a
cathode and a gate. When a suitable voltage is applied to the gate,
current flows between the anode and the cathode. However, an SCR
does not have the high current capability required to switch a high
voltage. Therefore, it is not suitable for many applications.
The gas discharge tube has been used where higher currents are
encountered. Gas discharge tubes are expensive to manufacture. They
are in the form of a sealed gas filled tube having anode, cathode
and trigger electrodes positioned within the tube. The tube is
designed such that a high voltage applied between the anode and the
cathode is insufficient to break down the gap between the anode and
the cathode. However, when a lower voltage is applied to the
trigger electrode, the breakdown voltage between the anode and the
cathode is reduced to below the applied voltage and a rapid
discharge occurs. A trigger energy of perhaps 0.5 millijoules may
control, for example, the discharge of 2 millijoules or more to
fire a munitions fuze, such as an exploding foil initiator
bridge.
Modern munitions have a solid state electronic fuze arming and
firing circuit. The overall circuit reliability is reduced and the
manufacturing cost is increased when a gas discharge tube is used
in conjunction with the arming and firing circuit. The gas
discharge tube is both expensive to manufacture and expensive to
install in the firing circuit. For a conventional gas discharge
tube, as many as 6 electrical connections must be made and the tube
must be physically mounted on the circuit board, for example, by
the use of clamps or solder or an epoxy adhesive. Further,
sufficient space must be provided for mounting the tube, which may
be relative large.
DISCLOSURE OF INVENTION
According to the invention, a munitions arming and firing circuit
is provided with a small integral solid state spark gap for
controlling the discharge of energy from a high voltage charged
capacitor to a fuze initiator, such as a slapper detonator
exploding foil initiator. The spark gap may be formed on the same
substrate on which the arming and firing circuit is formed and both
may be formed at the same time. The spark gap consists of an anode,
a cathode and a trigger electrode which are formed, for example,
with conventional thick film technology. The trigger electrode is
formed as a first layer on a dielectric substrate. The trigger and
the adjoining substrate are covered with a precisely controlled
dielectric pattern, as a second layer. A third precisely controlled
layer forms a separate cathode and anode. The cathode and anode
have a controlled spark gap between them and do not overlap the
trigger electrode. Optionally, a dielectric fourth layer may cover
part of the cathode and anode, so long as both are exposed at the
spark gap. For some applications, the above described spark gap may
operate exposed to the ambient atmosphere. For other application,
the spark gap is enclosed in a hermetically sealed structure which
may be filled with an inert gas such as nitrogen. The sealed
structure may be, for example, a ceramic cover fused, soldered or
otherwise bonded to the substrate and the electrodes.
The solid state spark gap functions similar to a gas discharge
tube. The anode and cathode are maintained at the same potential as
the charge on an energy storage capacitor. The voltage on the anode
and cathode is insufficient to break down the spark gap. However,
when a trigger pulse is applied to the trigger electrode, the gas
atoms above the trigger ionize to lower the spark gap breakdown
voltage to below the applied voltage. At this instance, the energy
is rapidly discharged across the spark gap to fire the fuze
initiator.
When the spark gap is integrally formed on the same substrate as
the arming and firing circuit, the manufacturing cost is reduced.
The spark gap is less expensive to manufacture than a gas discharge
tube. Conventional circuit manufacturing technology permits precise
orientation of the electrodes to achieve accurate triggering
voltages. Finally, the expenses of mounting the gas discharge tube
and of making the required electrical connections are
eliminated.
Accordingly, it is an object of the invention to provide an
improved spark discharge device for use, for example, in firing
munitions.
Other objects and advantages of the invention will be apparent from
the following detailed description and the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view of an improved spark gap according to the
invention;
FIG. 2 is a cross sectional view taken along line 2--2 of FIG. 1;
and
FIG. 3 is a view in cross section similar to FIG. 2, but
illustrating a modified form of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIGS. 1 and 2 of the drawings, a solid state spark gap
device 10 is shown according to the invention. The spark gap device
10 is formed on a dielectric substrate 11, which may be a ceramic
substrate or the foundation used for normal thick film circuit
processing techniques. In the preferred embodiment, the spark gap
10 device is formed from several layers sequentially deposited as
thick films on the substrate 11. A trigger electrode 12 is
deposited as a first layer. The trigger electrode 12 is formed from
an electrically conductive material. In the illustrated spark gap
10, the trigger electrode 12 has a generally rectangular body 13
connected to a terminal 14. However, it will be appreciated that
the body 13 may have other shapes.
A dielectric second layer 15 is deposited over the trigger
electrode body 13, an adjacent portion of the terminal 14 and a
predetermined adjacent area on the substrate 11. The second layer
15 is sufficiently large to provide space for an anode 16 and a
cathode 17. The dielectric second layer 15 is deposited with a
substantially uniform thickness. Consequently, the layer 15 will
have a raised portion 18 where it extends over the thick film
forming the trigger electrode 12. The anode 16 and the cathode 17
are deposited as separate portions of a third layer on the
dielectric second layer 15. The anode 16 and the cathode 17 are
electrically conductive layers deposited on the second layer 15 so
as to lie opposite the substrate 11 and not opposite the trigger
electrode 12. The anode 16 and the cathode 17 may be of identical
construction and are interchangeable in electrical connections to
adjoining circuitry. The anode 16 has a terminal end 22 and the
cathode 17 has a terminal end 23. The terminal ends 22 and 23 may
be on the second layer 15, as illustrated, or they may extend,
respectively, over edges 24 and 25 of the second layer 15 and onto
the substrate 11 for connecting directly to other circuitry (not
shown) on the substrate 11.
A spark gap 19 is formed between edges 20 and 21, respectively, of
the anode 16 and the cathode 17. The spark gap 19 extends over the
raised portion 18 of the dielectric layer 15 and, hence, extends
opposite the trigger electrode 12. For many applications, the solid
state spark gap device 10 will function adequately with no
additional components or layers. However, the device 10 must be
located where the spark gap 19 is protected from dust, moisture and
other contaminations which may lower or change the voltage required
to break down the spark gap 19. If the breakdown voltage is
lowered, the spark gap 19 may discharge prematurely.
If additional protection for the spark gap 19 is desired or
required by ambient conditions, a cover 26 may enclose the spark
gap 19. An optional fourth dielectric layer 27 may be deposited to
extend over a portion of the anode 16 and a portion of the adjacent
second layer 15. However, the layer 27 does not cover the spark gap
edge 20 or the terminal end 22 of the anode 16. Similarly, an
optional fourth dielectric layer 28 may be deposited to extend over
a portion of the cathode 17 and a portion of the adjacent second
layer 15. The layer 28 does not cover the spark gap edge 21 or the
terminal end 23 of the cathode 17. The cover 26 may be fused or
bonded to the fourth layers 27 and 28, the second layer 15 and the
substrate 11 with, for example, a sealing glass to form an enclosed
chamber 29 surrounding the spark gap 19. Of course, the cover 26
may be bonded in place by other means, such as by an epoxy resin.
The chamber 29 may be filled with dry air or with an inert gas such
as nitrogen for maintaining controlled conditions at the spark gap
19.
For operation of the spark gap device 10 in a firing circuit (not
shown), a predetermined potential is maintained between the anode
16 and the cathode 17 by a charged capacitor. At the proper time
and conditions, a trigger pulse is applied to the trigger electrode
12. The pulse on the trigger electrode 12 produces ionization of
some gas atoms in the spark gap 19, thereby lowering the breakdown
voltage across the spark gap 19 to below the potential applied
between the anode 16 and cathode 17. When discharge takes place
across the spark gap 19, the energy stored in the capacitor is
dumped to a load as a high current pulse of short duration. It
should be noted that the device 10 is particularly suitable for
single use applications, such as for firing or initiating
munitions. The solid state spark gap device 10 is not designed for
withstanding spark erosion which will occur under continuous high
current arcing. It was stated above that the anode 16 and the
cathode 17 are formed on the second layer 15 so as not to extend
opposite the trigger electrode 12 and that the spark gap 19 lies
opposite the trigger electrode 12. If the anode 16 and/or the
cathode 17 overlap the trigger electrode 12, the electric field
will be concentrated in the portions of the second layer 15 between
the overlapping anode 16 and/or cathode 17 and trigger electrode
12. As a consequence, a higher trigger voltage will be required to
initiate breakdown at the spark gap 19 because any given trigger
voltage will result in less ionization at the spark gap.
It will be appreciated that the solid state spark gap device 10 may
be manufactured using various known technologies. For example, the
device 10 may be manufactured by conventional thick film processing
techniques such as screen printing, drying and firing. Or, the
device may be manufactured using known processes involving the use
of a photoresist and selective etching techniques. Further, the
spark gap device 10 may be formed as an integral element on a
substrate which includes other circuitry, or it may be formed as a
separate element which can be connected to other circuitry.
One optional construction is illustrated in FIG. 3 where a first
conductive layer comprises the trigger 30, anode 31, and cathode 32
formed on the common substrate 34. These three electrodes are
electrically separated from one another, but are formed at the same
time on the substrate as one layer. A precisely controlled
dielectric 33 covers only the trigger 30 as a second layer. The
remaining construction would be as mentioned above with the spark
gap device of FIG. 3 differing from that of FIGS. 1 and 2 in that
the three electrodes 30, 31 and 32 are substantially coplanar
allowing for the elimination of one of the layer forming steps in
the process. Thus, the optional dielectric layers 35 and 36 (which
correspond to the fourth layer 27 and 28 in FIG. 2) are the third
layer in FIG. 3.
Various other modifications and changes to the above described
preferred embodiment of the solid state spark gap device 10 will be
apparent to those skilled in the art without departing from the
spirit and the scope of the following claims.
* * * * *